Reactor combustor, gasifier

Heat is transferred between the two reactors by circulating sand between the gasifier and combustor. Both reactors are of the riser type with a very short residence time. They allow for a high PVC waste throughput. The gasifiers have a reducing atmosphere, which prevents the formation of dioxins. 

Figure 2 shows the general arrangement of a gasifier/ reactor/combustor applied to a typical heating or power boiler. 

An important variant of the Fluid Bed system is under development. This variant eliminates use of air or oxygen in the actual gasifier. Steam and coal are the reactants. Since we know from Table 3 that the reaction of steam with coal is endothermic, a heat source must be provided. Hot solids in the form of char are heated in a combustor and are transferred to the gasification reactor as one these processes. In another, hot alkaline oxides react with the carbon dioxide in the gas to form carbonates. The exothermic reaction of carbonate formation supplies the heat requirements of the steam-carbon reaction. Both of these processes depend on a reactive coal or char to implement the steam-carbon reaction. 

Reactor Network Modeling of a Biomass Dedicated Swirling Combustor and a Fluidized Bed Gasifier... 

A central draft tube is used primarily for recirculating solids, and the dense, dry char collects in the fluidized bed at the top of the draft tube and is withdrawn at this point. Dolomite or calcium oxide (sorbent) is added to the fluidized bed to absorb the sulfur present as hydrogen sulfide in the fuel gas and spent sorbent is withdrawn from the bottom of the reactor and regenerated. The heat for devolatilization is supplied primarily by the high-temperature fuel gas produced in the gasifier combustor. After separation of fines and ash, product gas is cooled and scrubbed with water for final purification. 

In the combustion section, substantially all of the ash in the system is converted to molten slag, which is removed via the bottom of the gasifier. The remainder of the coal is fed to the reaction section of the gasifier where it is contacted with hot gases entering the reaction zone from the combustor. The gasification process takes place in the entrainment section of the reactor where the coal is devolatilized and reacts with the hot gases to produce the desired product gas. 

Important industrial applications for fluidized bed reactors are also discussed, including fluid catalytic cracking (Chapter 14), gasifiers and combustors (Chapter 15), chemical production and processing (Chapter 16), coating and granulation (Chapter 17), and ffuidized bed drying (Chapter 18). 

Fluidized bed gasifiers and fluidized bed combustors for carbonaceous fuels are relatively simple chemical reactors that can be utilized for several industrial applications that include chemical synthesis, process heat supply, steam generation, and power generation. Only relatively recently have carbonaceous fuel fluidized bed combustors and gasifiers reached or approached commercial status, with fluidized bed combustors gaining commercial acceptance earlier than fluidized bed gasifiers. 

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